Figure 3. Facilitation depends on intracellular polyamines.

A, washout of intracellular polyamines results in linearization of the I-V relation and disappearance of facilitation. Upper traces, currents in GluR-B(Q) channels, recorded around 1 min after patch formation, using pipette solution ‘b’, showed a 40 % steady-state facilitation (33 Hz) whereas 15 min later in the same patch, facilitation was no longer present. Holding potential was −60 mV. Lower panel, I-V relations, normalized to the current amplitudes at −80 mV, correspond to currents measured around 1 min (○) and 15 min (•) after patch formation (I-V recorded at 0.2 Hz). Qualitatively similar results were obtained in 11 patches. B, facilitation does not washout when spermine is added to the intracellular solution (pipette solution ‘b’ with added spermine (25 μM)). Same experimental protocol as in A. Upper traces, currents showed a steady-state facilitation of 23 and 29 % at 1 and 15 min, respectively, after patch formation. Lower panel, I-V relations correspond to currents measured around 1 min (○) and 15 min (•) after patch formation. Facilitation did not wash out in all 25 patches tested. Note that in both A and B the amplitude of the first current in the trains at 15 min was smaller due to current rundown which occurred during relatively long-lasting experiments regardless of the absence or presence of spermine in the pipette (in both instances, currents are reduced by about 50 %).